This project is designed to continue studies on the structure of steroid binding sites. The previously studied 20 Beta-hydroxysteroid dehydrogenase will be affinity labeled by 16 alpha-bromoacetoxyprogesterone and 21 alpha-bromoacetoxyprogesterone. Thereafter, specific enzymic hydrolysis will be carried out on each sample and finger printing will be done to see if the same histidyl residue is carbosymethylated by both steroids. Sequencing of the active site peptides will be carried out. The estrogen receptor from bovine (calf) uterus will be purified by the affinity chromatography methods of Puca and Cautrecasas for subsequent affinity-labeling studies using 2-bromacetoamidoestradiol 3-methyl ether, 4-bromoacetamidoestradiol 3-methyl ether and 16 alpha-bromacetoxyestradiol as well as other derivatives. Further affinity-labeling studies of human placental estradiol-17 Beta dehydrogenase will be carried out with 6-bromoacetoxyesterone and 11 Beta acetoxyestrone or their 3-methyl ether derivatives. These studies are designed to further our knowledge of the topography of steroid binding of maculamolecular steroid binding sites. BIBLIOGRAPHIC REFERENCES: R.C. Strickler, F. Sweet, & J. C. Warren: Affinity Labeling of Steroid Binding Sites: Study of the Active Site of 20 Beta-Hydroxysteroid Dehydrogenase with 2 alpha-Bromoacetoxyprogesterone and 11 alpha-Bromoacetoxyprogesterone. J. Biol. Chem. 250:19; p. 7656, 1975. C.-C. Chin, J.B. Dence & J.C. Warren: Crystallization of Human Placental Estradiol-17 Beta Dehydrogenase. J. Biol. Chem. 251:3700, 1976.